finish examples 2 and 3

examples/3_train_policy.py

@@ -1 +1,55 @@
-# TODO
+"""This scripts demonstrates how to train Diffusion Policy on the PushT environment.
+
+Once you have trained a model with this script, you can try to evaluate it on
+examples/2_evaluate_pretrained_policy.py
+"""
+
+import os
+from pathlib import Path
+
+import torch
+from omegaconf import OmegaConf
+from tqdm import trange
+
+from lerobot.common.datasets.factory import make_offline_buffer
+from lerobot.common.policies.diffusion.policy import DiffusionPolicy
+from lerobot.common.utils import init_hydra_config
+
+output_directory = Path("outputs/train/example_pusht_diffusion")
+os.makedirs(output_directory, exist_ok=True)
+
+overrides = [
+    "env=pusht",
+    "policy=diffusion",
+    # Adjust as you prefer. 5000 steps are needed to get something worth evaluating.
+    "offline_steps=5000",
+    "log_freq=250",
+    "device=cuda",
+]
+
+cfg = init_hydra_config("lerobot/configs/default.yaml", overrides)
+
+policy = DiffusionPolicy(
+    cfg=cfg.policy,
+    cfg_device=cfg.device,
+    cfg_noise_scheduler=cfg.noise_scheduler,
+    cfg_rgb_model=cfg.rgb_model,
+    cfg_obs_encoder=cfg.obs_encoder,
+    cfg_optimizer=cfg.optimizer,
+    cfg_ema=cfg.ema,
+    n_action_steps=cfg.n_action_steps + cfg.n_latency_steps,
+    **cfg.policy,
+)
+policy.train()
+
+offline_buffer = make_offline_buffer(cfg)
+
+for offline_step in trange(cfg.offline_steps):
+    train_info = policy.update(offline_buffer, offline_step)
+    if offline_step % cfg.log_freq == 0:
+        print(train_info)
+
+# Save the policy, configuration, and normalization stats for later use.
+policy.save(output_directory / "model.pt")
+OmegaConf.save(cfg, output_directory / "config.yaml")
+torch.save(offline_buffer.transform[-1].stats, output_directory / "stats.pth")